Photovoltaic modules (PV modules) are particular optoelectronic components. Photovoltaics (PV) is the direct conversion of radiant energy, principally the energy of the sun, into electrical energy with the aid of solar cells. There are various embodiments of solar cells, the most widespread being thick-layer silicon cells, either as monocrystalline cells (c-Si) or multicrystalline cells (mc-Si). Increasingly widespread are thin-film cells made of amorphous silicon (a-Si), GaAs (gallium arsenide), CdTe (cadmium telluride), CIS (copper, indium, selenium), CIGS (copper, indium, gallium, selenium), and also organic solar cells and dye cells.
For the purpose of obtaining energy, solar cells are usually connected to form large solar modules, known as PV modules. For this purpose the cells are connected in series with conductor tracks on the front and rear. This results in addition of the voltage of the individual cells. Moreover, the solar cells are typically processed as a laminate, that is, in particular, provided on the top and bottom sides with a barrier material (glass, films, etc.).
The manufacture of a solar module is frequently accomplished with the optically active side downwards. Generally a corresponding glass is cleaned and placed ready. The glass is typically a low-iron, tempered white glass in a thickness of 3 to 4 mm, with very low absorption between 350 nm and 1150 nm. Atop this glass then comes a cut-to-size sheet of ethylene-vinyl acetate film (EVA film). The solar cells are joined by means of solder ribbons to form individual strands (called strings) and positioned on the top side of this EVA film. Then the interconnects which are intended to connect the individual strings to one another and which lead to the site of the connection socket are positioned and soldered. Subsequently the whole is covered in succession with cut-to-size EVA films and polyvinyl fluoride films (e.g. Tedlar™) or with an assembly of EVA, polyester and polyvinyl fluoride. The next step in production is the laminating of the module under a reduced pressure of around 20 mbar and at around 150° C. At the laminating stage, the EVA film, which up to that point has been milky, turns into a clear, three-dimensionally crosslinked plastic layer that can no longer be melted, and the solar cells are embedded in this layer, and the layer is firmly connected to the glass screen and the back-side film. Following lamination, the edges are trimmed, the connection socket is fitted, and the laminate is populated with freewheeling diodes. The laminate is thus complete.
PV modules are provided, for reasons of stability, with a frame, more particularly an aluminium frame, which serves both for assembly and for protection of the PV modules from fracture as a consequence of excessive bending. The connection between frame and laminate, which typically comprises the glass, polymer films, back-side film and solar cells, is solved, for example, through the application of a double-sided foam adhesive tape. This tape is bonded typically to the laminate edge and optionally is also wrapped round on to the bottom and/or top sides of the laminate, where it is pressed down. The laminate thus equipped is then pressed with a very high force into the frame groove. The sensitive laminate, as already described above, is generally protected on its top side, i.e. the optically active side, by a glass layer against water vapour or water, and on the bottom side either by a second glass layer or by a film or film composite with barrier effect. The laminate edges, in contrast, are protected only by the foam adhesive tape against the ingress of water. As the PV modules grow in size, particularly in the case of tracker modules, i.e. modules which use motors to track the position of the sun, an ever greater force is required to press the laminates into the frames. Pressing is particularly critical at the edges of the laminate, since, in the case of wrapping or overlapping there is a double thickness of adhesive tape here. When the module is being pressed in, therefore, the adhesive tape may be damaged, possibly producing cracks in the foam, through which, in turn, rainwater may penetrate to the laminate edge and, by corrosion of the solder connections of the cell connectors, or by getting in beneath the glass/EVA boundary layer, may disrupt or even destroy the sensitive laminates. The operation of enframing using a double-sided foam adhesive tape proves to be very time-consuming and difficult to automate.
Alternatively the connection between frame and laminate may be realized by the introduction of crosslinkable liquid silicone or a liquid adhesive into the frame groove. This in turn has the disadvantage that the swelling silicone or the liquid adhesive requires laborious removal.
The present invention therefore addresses the problem of simplifying the assembly of a photovoltaic module, more particularly by mechanical application of the adhesive and/or by the introduction of the laminate into the PV frame at only low pressure. A further intention is that defects in the connection of frame and laminate, not least in the region of the frame corners, should be avoided.
An adhesive tape is proposed which is easy to apply and which simplifies frame assembly and which, furthermore, ensures a degree of protection of the laminate edge against water/water vapour penetration that is similar to that provided by the laborious sealing with crosslinkable liquid silicone.